Hydraulic master cylinder

ABSTRACT

The master-cylinder comprises a body defining a cavity therewithin, a bore opening into the cavity, a floating piston slidable in the bore to define a first chamber and a second chamber including the cavity, a spool valve for controlling fluid pressure in the second chamber upon actuation of a control rod, a lever mechanism interconnecting the rod, the piston and the valve for opening the latter, and a cut-off valve located in the first chamber for controlling the fluid flowing out from the first chamber. The cut-off valve includes a valve seat surrounding the outlet port of the first chamber and a valve member secured to a plunger slidable in an inner bore located in the floating piston, the inner bore opening at one end into said first chamber and at the other end into a compartment communicating with a low pressure reservoir and a spring biasing the plunger in abutment with a stop fixed relative to the floating piston.

ited States Patent [191 Papiau HYDRAULIC MASTER CYLINDER [75] Inventor: Guy Papiau, Arnouville les Gonesse, France [73] Assignee: Societe Anonyme D. E. A.,

Paris, France [22] Filed: Dec. 6, 1973 [21] Appl. No.: 422,216

[30] Foreign Application Priority Data Dec. 18, 1972 France 72.45051 [52] US. Cl 60/547, 60/582, 60/593 [51] Int. Cl. F15b 7/00 [58] Field of Search 60/547, 548, 550, 553, 60/568, 582, 589, 593; 91/391 R [56] References Cited UNITED STATES PATENTS 2,410,269 10/1946 Chouings 60/553 3,216,194 11/1965 Yardley 3,427,807 2/1969 Moyers..... 3,610,101 10/1971 Meyers 3,698,190 10/1972 Miyai 60/562 FOREIGN PATENTS OR APPLICATIONS 1,105,351 3/1968 France 91/391 R 6'2 64 63 -32 6''0 I 46 2a 38 3 l Dec. 24, 1974 Primary ExaminerPaul E. Maslousky Attorney, Agent, or Firm-Ken C. Decker; William N. Antonis ABSTRACT The master-cylinder comprises a body defining a cavity therewithin, a bore opening into the cavity, a floating piston slidable in the bore to define a first chamber and a second chamber including the cavity, a spool valve for controlling fluid pressure in the second chamber upon actuation of a control rod, a lever mechanism interconnecting the rod, the piston and the valve for opening the latter, and a cut-off valve located in the first chamber for controlling the fluid flowing out from the first chamber. The cut-off valve includes a valve seat surrounding the outlet port of the first chamber and a valve member secured to a plunger slidable in an inner bore located in the floating piston, the inner bore opening at one end into said first chamber and at the other end into a compartment communicating with a low pressure reservoir and a spring biasing the plunger in abutment with a stop fixed relative to the floating piston.

5 Claims, 1 Drawing Figure HYDRAULIC MASTER CYLINDER The invention relates to a hydraulic master-cylinder for supplying hydraulic pressure fluid to two independent utilising circuits, for example, two brake circuits in a motor vehicle.

Known master-cylinders comprise a body containing a bore in which two pistons are slidable, so as to define in the bore two independent pressure chambers for the pistons. One piston, known as the controlling or actuating piston, is connected to a controlling member, while the other floats in the bore in the body. Mastercylinders of this type have the disadvantage of considerably shortening the stroke of the controlling member in the event of failure of one of the utilising circuits connected to the pressure chambers.

An object of the invention is to provide a hydraulic master-cylinder in which the floating piston can be locked in position hydraulically in the event of failure of the circuit associated with the chamber defined between the bore end and the floating piston, so that there is a very substantial reduction in the idle movement of the controlling member when the other utilising circuits is operated.

The invention proposes a hydraulic master-cylinder for a split system having two separate utilising circuits, comprising a body with a bore therein, said bore having at one end a bottom, a floating piston slidably mounted in said bore to define therein a first pressure chamber, located between said piston and the bottom of said bore, and a second chamber, means for generating pressure into said second chamber upon actuation of an operator-operated controlling member, said first and second chambers communicating with said utilising circuits through first and second outlet ports respectively, and a cut-off valve controlled both by motions of the floating piston out of its idle position and by the fluid pressure in the first chamber, said cut-off valve impeding fluid to flow through said first outlet port when the fluid pressure in the first chamber, for a given motion of the floating piston, is less than a predetermined value.

An embodiment of the invention is described by way of example with reference to the single FIGURE, which represents a longitudinal section through a servo master-cylinder for a dual brake circuit in a motor vehicle.

The servo master-cylinder illustrated in the FIGURE comprises a body containing two parallel bores 12, 14 both leading into a cavity 16 closed by a cover 18. A floating piston 20 is mounted in the bore 12 and cooperates with the bottom 24 of this bore to define a primary pressure chamber 22 and with the cavity 16 to define a secondary pressure chamber 26. The two pressure chambers 22, 26 are connected by respective outlet orifices 28, 30 to two independent brake circuits (not shown) in a motor vehicle.

In accordance with the invention, the mastercylinder comprises a cut-off valve capable of preventing fluid from passing out of the primary chamber 22 towards the orifice 28. The cut-off valve comprises a valve member 32 capable of abutting directly on a seat 34 provided on the bottom of the body. As the FIG- URE shows, the valve member 32 comprises a cupshaped elastomeric portion 36 capable of masking the entrance 38 of the duct which connects the chamber 22 to the orifice 28. It should be noted that the elastomeric portion, in addition to ensuring a good seal when the valve is closed, permits the effective area of the cut-off valve to be selected as desired.

The valve member 32 is mounted in the body by way of a retractable resilient connection. In the embodiment illustrated, the valve member 32 is attached to a projection 39 belonging to a plunger 40, which is slidable in a fluid-tight manner in a longitudinal, blind bore 42 in the piston 20. This bore 42, of course, gives onto the pressure chamber 22. The plunger 40 and the end of the bore 42 together define a cavity 44 which communicates through radial orifices 46 with an annular space 48 situated between the fluid-tight bearing members 50, 52 of the piston. The space 48 normally communicates through passage 53 to port connected to a reservoir (not shown) for hydraulic brake fluid at low pressure (generally atmospheric pressure), so that if necessary the chamber 22 can be replenished by way of ducts 54 and by resilient lifting of a cup seal 56.

The retractable resilient connection also comprises a spring 58 bearing on the end of the bore 42 and urging the plunger 40 out of this bore onto a shoulder 60 fixed relative to the piston 20. The shoulder consists of the central portion of a sleeve 62, whose periphery 64 both provides an abutment for a piston return spring 66 and retains the resilient cup 56.

The return spring 66, which also bears on the body, urges the piston 20 into the idle position illustrated in the FIGURE, in which it bears on a stop 67 screwed on the body. In this idle position, when the brakes of the vehicle are off, the cut-off valve is open and the valve member 32 is a few millimetres off its seat, since the initial compression of the spring 66 is greater in this case than that of the spring 58.

The plunger 40 is used as means responsive to the fluid pressure in the primary chamber 22 so as to control the valve member 32. In order to balance the pressures acting on the valve member, the effective crosssection B of the plunger 40 is made substantially equal to the effective cross-section A of the cut-off valve.

The invention is described with reference to a servo master-cylinder which receives pressure fluid from a pressure source (not shown), an accumulator for instance, by way of a supply orifice 68 and discharges it through an orifice 70 connected to a low pressure reservoir (not shown). Since a brake assisting servo control mechanism of the same type, and its operation, are described in French Patent Specification No. 1,436,608, they will not be described in detail here.

The pressure rise in the fluid in the chamber 26 is controlled by a spool valve 72 mounted in a sleeve 73 fixed inside the bore 14. The valve 72 is moved by a mechanism 74 according to the relative motion of the piston 20 and of a controlling member 76 connected to the brake pedal of the vehicle. One end 92 of the member 76 projects into the second chamber 26 and is provided with a spline 43 adapted to receive parts of the mechanism 74. For sake of clarity only half of the end 92 is shown on the FIGURE and partially in dotted lines. The mechanism 74 essentially comprises, firstly, an arm 78 of which one end 80 is fork-shaped and pivoted on an element 82 and the other end is mounted on a pivot 83 fixed to the member 76 and, secondly, a double sensor 84, whose ends comprise cam-forming surfaces co-operating with the valve 72 and piston 20 respectively. The double sensor is pivoted on a pin 86 fixed to the arm 78. During normal assisted brake operation, the position of the element 82, which slides on a rod 88 attached to the cover 18, is fixed relative to the body. A spring 90 urges the element 82 onto a circlip mounted on the free end of the rod 88.

When the master-cylinder is in the idle position, as shown in the FIGURE, the brakes of the vehicle are off.

During normal assisted operation, a given shift of the push rod 76 is accompanied by a given shift of the piston and pressurisation of the chambers 22, 26. The ratio between the stroke of the push rod 76 and that of the piston 20 is slightly less than unity in the present case, as the piston moves faster than the push rod. This stroke ratio is a function of the lever arm ratio of the arm 78 (that is to say, the position of the pivot 86 relative to the points at which the ends 80, 81 are pivoted) and the lever arm ratio of the double sensor. In the event of a failure of assisted braking, for example due to rupturing of the circuit associated with the secondary chamber 26 or jamming of the slide valve 72, the spring 90 is compressed to enable the mechanism 74 to retract without being damaged when the free end 92 of the push rod 76 operates the piston 20 by direct engagement.

Since the push rod 76 follows the motion of the piston 20, the idle movement of the push rod remains short when the pressure rise in the chamber 26 fails, so that the designer can easily make the whole brake pedal stroke long enough for the pedal to conveniently operate the piston directly.

When the piston 20 is moved out of its idle position by the pressure fluid in the secondary chamber 26, the pressure rises in the primary chamber 22 and acts on the plunger 40, compressing the spring 58 since the fluid pressure in the cavity 44 remains close to atmospheric pressure. The resilient connection between the piston and the valve member therefore retracts. Motion of the piston towards the bottom 24 of bore is accompanied by relative motion of the piston 20 and valve member 32 in the opposite direction. The spring 58 is so calibrated in relation to the absorption characteristics of the utilising circuit associated with the chamber 22 that the cut-off valve does not close during normal operation corresponding to a pressure rise in chamber 22 upon shifting of piston 20. The calibration of the spring 58 is such that for a given pressure in the chamber 22, depending on the piston stroke and on the absorption in the circuit, there is relative motion of the valve member 32 towards the piston 20 at least equal to the said stroke. In practice it is desirable to have little absolute motion of the valve member 32 relative to the body, in order to minimise the idle movement of the piston 20 in the event of pressure failure in chamber 22. Clearance is also provided between the valve member 32 and its seat 34 to prevent undesired closing of the valve during the temporary pressure rise phase. The brakes in the circuit associated with the chamber 22 therefore operate properly. The same applies when the piston 20 is operated directly by the push rod 76.

If there is a failure in the brake circuit associated with the chamber 22, the fluid pressure falls in this chamber, producing additional movement of the piston 20 towards the bottom 24 of the bore and also extension of the retractable connection between the valve member and piston. These two movements are both in the same direction relative to the body in this event, and so the cut-off valve closes. (lt closes all the faster because the clearance between the valve member and its seat remains small while the master-cylinder is operating correctly). As the effective cross section A of the valve is substantially equal to the effective cross section B of the plunger 40, the assembly formed by the valve member and plunger is pressure-balanced. The compression of the spring 58 ensures that the elastomeric ring 36 stays in fluid-tight contact with the bore end 24. The fluid in the chamber 22 is trapped, and the piston 20 is locked in position hydraulically. Operation of the circuit associated with the chamber 26 continues in spite of the immobilisation of the piston 20, without the driver of the vehicle perceiving any abrupt, and highly unpleasant, depression of the brake pedal. Thanks to this feature the control of the spool valve remains smooth thereby avoiding any sudden change of pressure in pressure chamber 26 and a jerky operation of the corresponding brakes. In addition, the shortening of the stroke of the pushrod 76 due to the invention makes it possible to reduce the angle of maximum deflection of the arm 78 about its end 80 and thereby to simplify the design of the mechanism 74, particularly the length of the cam-forming surface on the double sensor.

The invention may also be applied to a non-servo tandem master-cylinder. In another embodiment of the invention (not shown), the master-cylinder comprises a body containing a bore in which two pistons are slidable so as to define two independent pressure chambers in the bore. One of the pistons, termed the controlling piston, is connected to the controlling member, whereas the other floats in the bore.

The floating piston is associated with a cut-off valve of the type described above, so as to control the discharge of fluid from the primary chamber defined be tween the floating piston and the bore end. In the event of failure of the utilising circuit associated with the primary chamber, hydraulic locking of the floating piston in position permits the pressure to rise in the other chamber without appreciably shortening the stroke of the controlling member. The driver then has a long enough pedal stroke for correct operation of the brake circuit which is still operative.

I claim:

1. In a hydraulic brake actuating device:

a housing defining a bore therewithin;

a piston slidably mounted in said bore and cooperating with opposite ends of the latter to define a pair of pressure chambers;

an outlet communicating with one of said chambers valve means shiftable from a condition venting the other chamber to a fluid reservoir to a position communicating said other chamber with a source of fluid pressure to thereby shift said piston to develop fluid pressure in said one chamber; and

a pressure differential responsive plunger having a pair of opposed faces slidably mounted on said piston, and resilient means yieldably urging said plunger to a predetermined position with respect to the piston, one of said faces being exposed to the fluid pressure level in said one chamber, the other face of said plunger being communicated with the fluid pressure level in said resevoir; and

cut-off valve means carried by said plunger for cooperation with said outlet to terminate communication therethrough when the fluid pressure level in said one chamber drops below a predetermined level for a given movement of the piston.

2. The invention of claim 1:

said piston defining a cavity opening into said one chamber, said plunger being slidably mounted in said cavity and cooperating with the end of the latter to define a fluid-receiving compartment, said compartment being communicated to said reservoir.

3. The invention of claim 2; and

a valve seat circumscribing said outlet, the crosssectional area of said valve seat being substantially equal to the cross-sectional area of said plunger;

said cut-off valve means sealingly engaging said valve sponding shoulder on the plunger. 

1. In a hydraulic brake actuating device: a housing defining a bore therewithin; a piston slidably mounted in said bore and cooperating with opposite ends of the latter to define a pair of pressure chambers; an outlet communicating with one of said chambers valve means shiftable from a condition venting the other chamber to a fluid reservoir to a position communicating said other chamber with a source of fluid pressure to thereby shift said piston to develop fluid pressure in said one chamber; and a pressure differential responsive plunger having a pair of opposed faces slidably mounted on said piston, and resilient means yieldably urging said plunger to a predetermined position with respect to the piston, one of said faces being exposed to the fluid pressure level in said one chamber, the other face of said plunger being communicated with the fluid pressure level in said resevoir; and cut-off valve means carried by said plunger for cooperation with said outlet to terminate communication therethrough when the fluid pressure level in said one chamber drops below a predetermined level for a given movement of the piston.
 2. The invention of claim 1: said piston defining a cavity opening into said one chamber, said plunger being slidably mounted in said cavity and cooperating with the end of the latter to define a fluid-receiving compartment, said compartment being communicated to said reservoir.
 3. The invention of claim 2; and a valve seat circumscribing said outlet, the cross-sectional area of said valve seat being substantially equal to the cross-sectional area of said plunger; said cut-off valve means sealingly engaging said valve seat to terminate communication through said outlet.
 4. The invention of claim 3; and means On said piston and on said plunger defining stop means for establishing the rest position of said plunger; said resilient means yieldably urging said plunger toward said rest position.
 5. The invention of claim 4: said means defining said stop means being a shoulder carried by said piston cooperating with a corresponding shoulder on the plunger. 